Fuse plug



May 4, 1937- F. J. MCHUGH 2,079,462

FUSE PLUG Original Filed June 30, 1933 2 Sheets-Sheet 2 Patented May 4, 1937 UNITED STATES PATENT GFFICE FUSE PLUG Application June so, 1933, serial No. 678,404 Renewed September 24, 1936 Claims.

My invention relates in general to protective devices for electrical circuits and has more particular reference to safety breakers or cutout devices for interrupting the circuit when the same becomes overloaded.

An important object of the invention is to provide a circuit breaker of the type having a current-carrying conductor, which, when overload conditions are set up, is adapted to rupture and open the protected circuit.

My present invention contemplates the provision of a circuit interrupter in which the current-carrying conductor may be replaced in position to render the device again effective for further use in a circuit after the conductor means has been ruptured in interrupting an overloaded circuit.

Another important object is to provide a device of the character described in a form adapted for insertion in the ordinary commercial power circuits.

Another important object is to utilize mercury or similar uid current-carrying medium as the rupturable element of the cutout device, the device being arranged to normally receive the fluid current-conducting medium in position to complete the electrical circuit with which the device is associated and the medium being arranged for expulsion from the circuit-making position when overload conditions prevail in the circuit and being readily returnable to circuit-completing position by a simple movement imparted to the device.

Another object is to provide a circuit breaker of the character mentioned, in which the circuitmaking medium may not return to circuit-completing position unless and until the device is manipulated for this purpose.

Another important object is to provide a cutout device of the character described having a relatively restricted channel, in which the circuitmaking medium extends when in circuit-completing position, and from which the medium may be expelled in order to interrupt the circuit, the

- device being arranged to confine arcing in said restricted channel.

Another important object is to provide a simple and substantial device of the character mentioned which may be used an indefinite number of times without being replaced.

Another important object resides in the simplicity and construction of the cutout devices, the same being inexpensive and easily manufactured, yet having rugged and reliable operating characteristics.

(Cl. o- 113) Another object is to utilize the blowout effect of mercury in a capillary channel as an overload circuit breaker.

Another object is to utilize surface tension of a fluid, such as mercury, to hold the conducting medium in operative circuit-making position until overload conditions prevail and out of operative position after the fuse has been blown.

Another object is to provide a channel having a restricted arcing portion and an enlarged blowout receiving channel interconnected by a tapering channel portion whereby to normally prevent the blowout medium from returning to operative position in the restricted channel' portion after being blown into the enlarged portion.

Another object is to utilize the natural adhesive eiect of mercury on certain metals to help hold the mercury in position.

Another object is to provide a device of the character described having means to indicate whether the circuit breaker is in operative or inoperative condition.

Another object resides in providing a novel sight indicator for the device.

Another object is to provide an outlet plug having a built-in overload circuit breaker.

Numerous other objects and advantages of the invention will be apparent from the following description, which, taken in connection with the accompanying drawings, discloses preferred embodiments of the invention.

Referring to the drawings:

Figure 1 is a side elevation of a preferred form of renewable circuit breaker embodying my present invention;

Figures 2 and 3 are sectional views taken substantially along the lines 2-2 and 3 3 respectively in Figure 1;

Figure 4 is a longitudinal section illustrating a modied construction embodying my present invention;

Figure 5 illustrates the manner of manipulating the cutout device in order to replace the current-carrying medium in operative position after the same has been expelled in opening the circuit in response to overload conditions;

Figure 6 shows a preferred form of sealing means for the chamber of the breaker;

Figure 7 is a sectional View showing a cartridge type breaker embodying my present invention;

Figure 8 is a sectional view showing an outlet socket plug having incorporated therein a breaker embodying my invention; and

Figures 9 and 10 are sectional views taken substantially along lines 9 9 and IU-Ill in Fgures 10 and 9 respectively and showing an outlet plug embodying my present invention.

To illustrate my invention, I have shown on the drawings, in Figures 1 5, a circuit breaker of the character commonly known as a blowout fuse, and, although my invention is not necessarily restricted to any particular embodiment, I have shown a plug form especially well adapted for use in fuse receptacles of the character cornrnonly used in commercial power circuits.

The invention, however, is adapted to other forms, more particularly, as shown in Figures '1-10, the invention may be incorporated in the so-called cartridge type fuse, in power outlet sockets, and in outlet plugs. In any event, the invention involves the utilization of a restricted channel into which a quantity of a suitable current-carrying medium, such as mercury, may enter and be normally retained in position to form an operative current carrying path between spaced terminals, the mercury being ejected from operative position when overload conditions prevail to interrupt the current-carrying circuit and being returnable to operative position after expulsion in response to the application of external forces to the device.

The circuit interrupter or fuse, shown in Figures l5, comprises a body of any suitable insulating material, preferably porcelain and preferably monolithic, although the body may be formed in interconnected sections if desired. The body is preferably of general cylindrical shape and may, if desired, be formed at one end with an enlarged portion |3, the surfaces of which are preferably roughened or knurled to provide a grip for the manipulation of the device including the insertion thereof in a fuse socket. 'Toward the opposite end of the body, the same iis formed to receive a preferably threaded conductor il, which, as shown in the drawings, comprises a sheet metal shell by means of which the device may be electrically and mechanically secured in a threaded fuse socket.

The body is also provided with one cr more channels preferably extending longitudinally of the body and containing a quantity of a suitable current-carrying medium, such as mercury. The opposite ends of the channels preferably open at the opposite ends of the body and are hermetically sealed to prevent the mercury from oxidizing. In the form shown in Figures 1, 2, and 3, the single channel is concentric with the axis of the body and comprises an enlarged portion I9 at one end, a restricted portion 2| at the other end, and an intermediate portion. 23 of tapering form. which interconnects the enlarged and restricted channel portions.

The channel portions may be formed in suitable manner as by coring or by boring the enlarged and intermediate portions at one end of the body while the restricted channel portion 2l is bored from the other end. The enlarged channel portion |9 also preferably opens at the end of the body which is provided with the gripping portion |3, the end face of the body being preferably counter-sunk as at 25. The restricted channel portion 2| also preferably opens at the end of the body opposite from the enlarged gripding portion i3.

The body i is provided with an enlarged socket 21 opposite the open end of the restricted channel 2! and a plug 29 of any suitable current-carrying material is seated in the socket 2l with its inner face closing the open end of the restricted channel portion 2|, the plug 29 any being secured in the socket 21 by means of a suitable cementing material 3|, or the plug may be threaded or otherwise mechanically secured in place in the socket.

The sides of the restricted channel 2| are also preferably enlarged slightly as at 33 adjacent the face of the plug which closes the open end of the channel, or the plug itself may be formed with an opening in its face opposite the end of the channel in order to form a better Contact with the current-carrying medium.

The plug 2S also has an outer surface 35, which projects slightly beyond the end of the body il in order te form a central terminal whereby contact may be made with a terminal of the socket in which thc device is secured. It will be noted` that this construction exposes a portion of the plug 29 in the channel 2|. A second contact member or terminal 31 is exposed in the channel in spaced relationship with the exposed portions of the plug 2Q. This second terminal is prelerably arranged in the body with its inner .tace exposek in the channel preferably at thc tapering portion 23, the outer end of the termilnal 31 forming contact with the conductor i1 by means of which an electrical connection may be formed between the terminal 31 and a termi .nal of the fuse-supporting socket, in which the device is adapted for insertion.

A quantity of mercury or other suitable current-conducting fluid 39 is enclosed in the channel, the quantity of uid being sufficient to ll the restricted channel 2| and enter the enlargements 33 in order to form a current-conducting path between the surfaces of the terminals 29 and 31, which are exposed in the channel. The fluid-carrying medium may be inserted in the channel through the open end of the enlarged channel portion I9 which may then be sealed in any suitable manner as by the plug 4| cemented in place in a socket 43 formed in the bottom of the countersunk portion 25 at the open end of the enlarged channel portion I9.

I prefer to use mercury as the fluid-carrying medium for electrically bridging the space between the terminals 29 and 31 in the channel and to form the terminals 29 and 31 of copper or a copper alloy with which the mercury may form a relatively weak bond sufficient to hold it in place after being forced into the restricted channel 2| between the terminals. The mercury also has a natural surface tension which will assist in holding the position illustrated in Figure 2 of the drawings. The restricted channel portion 2 however, is preferably of a size which will normally prevent the mercury from flowing into the channel, the natural tension of the mercury tending to prevent the same from flowing into the restricted channel. The tendency of the mercury to refrain from entering the channel 2! may, however, be overcome by shaking the device in the manner illustrated in Figure 5 of the drawings. By so shaking the device, the mercury may be caused to flow from the enlarged channel portion |9 into the restricted portion, that is to say, into operative position forming an electrical connection between the terminals 29 and 31. When the mercury has been so arranged in operative position, its natural surface tension, together with its tendency to form a bond with the terminals, will normally prevent the mercury from owing out of the restricted channel and into the enlarged channel. The device may then be arranged in a fuse holder by simply screwing the threaded portion I1 into the fuse-holding socket. When an overload occurs, the mercury will become heated and will be expelled from the restricted channel portion 2| into the enlarged portion I9, thus breaking the electrical connection between the terminals 29 and 31 and interrupting the circuit in which the device is mounted. The mercury after such expulsion will not ordinarily return to operative position in the restricted channel portion 2| but can be easily repositioned for operation by removing the device from the fuse socket and by applying external forces as by shaking the device in the manner heretofore described and illustrated in Figure of the drawings. The device can thus be used more or less indefinitely without wearing out.

I prefer to form the sealing plug 4| of transparent material to form a window through which the position of the mercury in the channel 'may be observed from outside. The window may be .formed as a at disk of glass, mica or other suitable material cemented in place to hermetically seal the fluid medium in the channel but I prefer to form the window as an open ended shell 45, as shown in Figure 6. The open end of the shell is sealed in communication with the channel I9 with the dome of the shell protruding out of the socket 43. The shell is also necked in between its open end and the top of the dome so that when the mercury is expelled from circuit-'making position in the channel, it will be forced into the dome of the shell and held there, in full view, by the action of the restricted neck in conjunction with the surface tension of the mercury. Ihe position of the mercury can thus be determined simply by inspection and the mercury can be ejected from the dome and returned to operative position in the channel portion 2| simply by shaking the device.

By hermetically sealing the mercury in the channel, it is prevented from oxidizing and thus 4rendering the fuse inefficient. Slight oxidation may be caused by the oxygen in the air originally trapped in the channel but this will be quickly eliminated without any deleterious effect in the fuse after which the atmosphere within the channel will be mainly inert.

In Figure 4 of the drawings, the body is provided with a plurality of channels 20, each having an enlarged portion I9, a restricted portion 2|, and an intermediate tapering portion 23, the open ends of the restricted portions 2| are slightly enlarged as at 33 and closed by means of the plug 29 and each channel is provided with a preferably radially extending terminal which is exposed at the tapering portion and electrically connected with the conductor member I1, each channel having a body of fluid conducting medium 39 adapted to i'lll the restricted channel fl* portion and form a connection between the Aterminals 29 and 31. The open ends of the enlarged channel portions are sealed by means of the members 4|. The device operates in a fashion similar to that having the single channel 20 but provides a circuit breaker of higher current-carrying capacity. f

The capacity of the device may also be varied to a certain extent by changing the size of the channel 2| but for heavy duty breakers, I prefer to use a plurality of channels connected in parallel in the circuit. f

In Figure 7 of the drawings, I have shown the invention as embodied in a so-called cartridge type fuse. In this form, the body is preferably cylindrical and the channel 20 is formed longitudinally of the cylindrical body with the enlarged portion I9 opening at one end and the restricted portion 2| at the other end of the body, the restricted portion opening into an enlarged socket 21 in which is mounted the plug 29, the plug being held in place by means of the cement 3|. The restricted channel 2| also is or may be slightly enlarged as at 33 in the vicinity of the surface of the plug, or the surface of the plug may be hollowed out, as shown in dotted lines at 34, in order to improve the contact between the face of the plug and the mercury column in the channel.

The electrode, corresponding to the electrode 31 of the form shown in Figures 1 through 5 of the drawings, has a contacting portion mounted at the tapering portion 23 of the channel and has an arm i1 extending along a side of the enlarged channel portion I9 to the outer end of said channel portion, the opposite ends of the body I| are provided with ferrules 49 which are secured to the body as by means of the cement 5|, or the sides of the body may be threaded, as at 52, to receive the ferrules. The threaded connection is preferred where the body I I is formed of bre, while cemented ferrules may be used where the body is formed of porcelain. The ferrules are also preferably soldered to the plug 29 and to the end of the arm 41. The ferrules also may be provided with knife blades 53 if it is desired to mount the fuse in a holder having knife blade supports. The operation and manipulation of the fuse is similar to that heretofore described in connection with the fuse illustrated in Figures 1 through 6.

In Figure 8, I have illustrated an outlet device 55 adapted to receive the prongs 51 of an outlet plug 59 and connect the prongs in the electrical circuit in which the outlet device is mounted.

The outlet device incorporates a circuit breaker embodying my present invention and comprises a generally cylindrical body similar in form to the body II of the device illustrated in Figures 1 through 6. The body is provided with the breaker channel having an enlarged portion I9, the tapering portion 23 and a restricted portion 2|, the restricted portion being sealed at one end of the device by means of the terminal plug 29 held in place by means of the cement 3|. The open end of the breaker channel 20 is sealed in any suitable or convenient manner as by means of the sealing disk 4I. The body of the device is formed with a pair of channels 6| on opposite sides of the breaker channel 20. One of these channels communicates with the channel con taining the terminal 31, while the other channel communicates with the side of the body behind the threaded shell I1 and each channel 6| contains a spring contact 63 in position to engage and form an electrical connection with the prongs 51 of the plug 59 when the same are inserted in the channels 6|. One of the spring contacts 63 extends through its channel and forms an electrical connection with the shell I1, while the other spring contact forms an electrical contact with the terminal 31. The terminal 31 in the device shown in Figure 8 does not engage the shell I1 as is the case in the forms shown in Figures 1 through 6 but the outer end of the terminal is removed and the space in the channel between the shell |1 and the terminal is sealed with any suitable insulating compound 65 after the terminal 31 and its associated spring terminal 63 have been assembled.

The space in the channel through which the other spring terminal 63 extends into engagement with the shell lI is also preferably sealed with a suitable insulating compound in order to hold said spring terminal in place after insertion. When the circuit-making fluid 39 is in position as shown in Figure 8, forming a circuit between the plug 29 and the terminal 3T, one of the prongs of the plug will be electrically connected through the shell il', while the other prong will be connected through the terminal 31, the mercury column 39 and the terminal plug 29. The operation of the circuit breaker is similar to that heretofore described in connection with the device shown in Figures 1 through 6.

In Figures 9 and l0, I have shown a circuit breaker embodying my present invention as incorporated directly in a pronged plug adapted for insertion in an outlet socket.

The device shown in Figures 9 and 10 cornprises a body ll of any suitable insulating material provided with the channel 20 having an enlarged portion I9, a restricted portion 2l, and an intermediate tapering portion 23, the open end of the restricted channel portion 2| being closed by the terminal plug 28 which is held in place in the socket 27 as by means of the cement i, the open end of the enlarged channel portion l being sealed in any suitable manner as by the sealing member 4|. The body 'Il has a channel i3 orfled therethrough to receive a cable, one wire of which is electrically connected to the prong which is secured to the body H in any suitable manner. The body also carries a prong 'l'l secured thereto in parallel spaced relationship with respect to the prong 'll and the prong 19 is connected as by the contacting screw 8l with the terminal 3l, the outer end of which is relieved as in the forni of the device shown in Figure 8 in order to permit a sealing compound 65 to be ari anged in the channel containing the terminal in order to protect the terminal from exposure cn the side oi the body ll. The inner face of the terminal 'il is exposed in the circuit breaker channel 2Q preferably at the tapering portion 23. The other conductor of the cable l5 is electrically connected to the terminal plug 29.

It is tho ht that the invention and numerous of its atte -dant advantages will be understood from the foregoing description and it is obvious that numerous changes may be made in the form, consfuucI n, and arrangement of the several hout departing from the spirit or scope ention or sacrificing any of its attendrit-ages; the forms herein described beferred embodiments for the purpose of ting my invention.

ng thus described my invention, what I new and desire to secure by Letters ahnt is as follows:

l. A circuit interrupter comprising a body of .ting material having a channel including a restricted channel portion, a pair of spaced ,oc-.es exposed in said restricted 'channel portion, a iiuid electrical conducting medium in said channel and adapted to enter the restricted nnel portion and form a conducting path bei the electrodes, contact-making prongs on said body and electrically connected with said electrodes and adapted for insertion in the slots of an outlet socket whereby to provide means for electrically connecting the electrodes with the conductors of the socket.

2. A circuit interrupter comprising a body of insulating material having a channel including a restricted channel portion, a pair of spaced electrodes exposed in said restricted channel portion, a iluid electrical conducting medium in said channel and adapted to enter the restricted channel portion and form a conducting path between the electrodes, said body being formed to receive the prongs of an outlet plug, contactors to engage the prongs, means to electrically connect at least one of the contactors and one of said electrodes in an external circuit, and means to electrically connect the other contactor with the other electrode.

3. A circuit interrupter comprising a body of insulating material having a channel including a restricted channel portion, a pair of spaced electrodes exposed in said restricted channel portion, a uid electrical conducting medium in said channel and adapted to enter the restricted channel portion and form a conducting path between the electrodes, and contact-making elements on said body and adapted for connection in an external electrical circuit, means electrically connecting at least one of said contactmaking elements with one of said electrodes, a channel in said body for receiving a cable having a plurality of conductors, means to electrically connect one of the conductors of said cable with the other of said contact-making elements, and means to connect the other conductor of said cable with the other electrode.

4. A circuit interrupter comprising a body of insulating material having a channel extending from end to end of said body, said channel being restricted at one end and enlarged at the other. means forming a translucent window closing the enlarged end of said channel, an end electrode closing the restricted end of the channel, said electrode being exposed on one side in said channel and on the other side exposed outwardly of the end of said body, an intermediate electrode exposed in said channel substantially at the junction of the restricted and enlarged channel portions, a contact-making element carried on and exposed outwardly of said body, and means electrically connecting the intermediate electrode with said contact-making element.

5. A circuit interrupter comprising a body of insulating material formed with a cavity providing a chamber within said body, said body being formed with restricted ducts communicating with said cavity and extending to an opening on the surface of said body, terminal means closing the ends of said ducts and exposed therein, electrode means communicating with each duct at its junction with said cavity, a fluid electrical conducting medium in said cavity and adapted to enter the restricted ducts at their points of communication with said cavity, and a contact-mak ing element on said body and exposed outwardly thereof and electrically connected with said electrode means.

FRANK J. MCHUGH. 

